This invention relates to methods of forming integrated circuitry, to methods of forming elevated source/drain regions of a field effect transistor, and to methods of forming field effect transistors.
As integrated circuitry device dimensions continue to shrink, problems such as short channel effects, source-drain punchthrough, and hot electron susceptibility become ever present, particularly in the deep sub-half-micron regime. These effects have, in the past, been addressed by additional masking levels and through the incorporation of lightly doped drain (LDD) engineering.
This invention arose out of concerns associated with providing improved integrated circuitry devices while reducing problems associated with short channel effects, source-drain punchthrough, and hot electron susceptibility, particularly in the deep sub-half-micron regime.
Methods of forming integrated circuitry, methods of forming elevated source/drain regions, and methods of forming field effect transistors are described. In one embodiment, a transistor gate line is formed over a semiconductive substrate. A layer comprising undoped semiconductive material is formed laterally proximate the transistor gate line and joins with semiconductive material of the substrate and comprises elevated source/drain material for a transistor of the line. Subsequently, conductivity-modifying impurity is provided into the elevated source/drain material. In another embodiment, a common step is utilized to provide conductivity enhancing impurity into both elevated source/drain material and material of the gate line. In another embodiment, the undoped semiconductive layer is first patterned and etched to provide elevated source/drain regions prior to provision of the conductivity-modifying impurity. In another embodiment, the semiconductive material is first patterned, with conductivity-modifying impurity being subsequently provided into selected portions of the semiconductive material. Undoped semiconductive portions are subsequently removed selectively relative to doped semiconductive material portions.